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W E Wright

Publications and source records attributed to W E Wright.

At least 73 records · Page 4Linked to original sources
PubMed1997

Telomerase activity in ordinary meningiomas predicts poor outcome.

Telomerase, the enzyme that stabilizes telomere length, is reactivated with almost all cancer types, and it may be necessary for unlimited cell proliferation. Assessment of malignancy in ordinary meningiomas is inconclusive because no clear-cut correlation exists between aggressive clinical behavior and histological features or karyotypic abnormalities. We analyzed telomerase activity in 52 cases of meningioma by using the highly sensitive telomeric repeat amplification protocol and then compared clinical behavior in telomerase-positive and -negative ordinary meningiomas. Twenty-six of the 52 tumors (50%) had detectable telomerase activity. Twenty-one of the 22 neoplasms classified as malignant or atypical (95%) had detectable telomerase activity, and these tumors generally had a poor outcome. Interestingly, 5 of 30 ordinary (morphologically benign) meningiomas (17%) also showed detectable telomerase activity. Of the 5 patients with telomerase-positive ordinary meningiomas, 3 had rapid regrowth of the tumor despite gross total resection. The remaining 2 patients also had other primary malignancies. We observed a highly significant correlation in ordinary meningiomas between the presence of telomerase activity and a poor prognosis for the patient (P = .0002). Telomerase activity in benign meningiomas is clinically relevant because the presence of the enzyme suggests that these benign-appearing tumors may contain a population of immortal cells. The detection of telomerase activity may help to identify benign meningiomas that would be more likely to continue to grow and to recur clinically if surgical resection were incomplete.

Adolescent↗
PubMed1997

Multiple pathways for the regulation of telomerase activity.

The ends of vertebrate chromosome are composed of large tracts of a repeated sequence, TTAGGG, which are known as telomeres. Normal somatic cells progressively lose telomeric repeats with each successive cell division due to incomplete replication. Immortal and cancer cells compensate for telomeric loss by expressing the enzyme telomerase, an RNA-dependent DNA polymerase that maintains telomere length. Telomerase activity has been detected in almost 90% of all human cancers. Telomerase activity is generally absent in normal somatic tissues but is detected in adult testes, activated lymphocytes, and lower levels are expressed in proliferative cells of renewal tissues. Telomerase activity is downregulated in cells that exit the cell cycle via either terminal differentiation or (reversible) quiescence. Inhibition of telomerase activity in tumour cells may provide an effective way to treat cancer by potentially reducing the recurrence of tumours due to occult micro-metastases. An understanding of the pathways involved in telomerase regulation will be important for determining the most practical means of inhibiting its activity.

Cell Division↗
PubMed1997

Reconstitution of human telomerase with the template RNA component hTR and the catalytic protein subunit hTRT.

The maintenance of chromosome termini, or telomeres, requires the action of the enzyme telomerase, as conventional DNA polymerases cannot fully replicate the ends of linear molecules. Telomerase is expressed and telomere length is maintained in human germ cells and the great majority of primary human tumours. However, telomerase is not detectable in most normal somatic cells; this corresponds to the gradual telomere loss observed with each cell division. It has been proposed that telomere erosion eventually signals entry into senescence or cell crisis and that activation of telomerase is usually required for immortal cell proliferation. In addition to the human telomerase RNA component (hTR; ref. 11), TR1/TLP1 (refs 12, 13), a protein that is homologous to the p80 protein associated with the Tetrahymena enzyme, has been identified in humans. More recently, the human telomerase reverse transcriptase (hTRT; refs 15, 16), which is homologous to the reverse transcriptase (RT)-like proteins associated with the Euplotes aediculatus (Ea_p123), Saccharomyces cerevisiae (Est2p) and Schizosaccharomyces pombe (5pTrt1) telomerases, has been reported to be a telomerase protein subunit. A catalytic function has been demonstrated for Est2p in the RT-like class but not for p80 or its homologues. We now report that in vitro transcription and translation of hTRT when co-synthesized or mixed with hTR reconstitutes telomerase activity that exhibits enzymatic properties like those of the native enzyme. Single amino-acid changes in conserved telomerase-specific and RT motifs reduce or abolish activity, providing direct evidence that hTRT is the catalytic protein component of telomerase. Normal human diploid cells transiently expressing hTRT possessed telomerase activity, demonstrating that hTRT is the limiting component necessary for restoration of telomerase activity in these cells. The ability to reconstitute telomerase permits further analysis of its biochemical and biological roles in cell aging and carcinogenesis.

Amino Acid Sequence↗
PubMed1997

Telomerase activity concentrates in the mitotically active segments of human hair follicles.

Telomerase is a ribonucleoprotein enzyme capable of adding hexanucleotide repeats onto the ends of linear chromosomal DNA. Whereas normal somatic cells with a limited replicative capacity fail to express telomerase activity, most immortal eukaryotic cells do. Cells of renewal tissues (e.g., skin, intestine, blood) require an extensive proliferative capacity. Some cells in such renewal tissues also express telomerase activity, most likely to prevent rapid erosion of their telomeres during cell proliferation. In this study, we measured the levels of telomerase activity in dissected compartments of the human hair follicle: hair shaft, gland-containing fragment, upper intermediate fragment (where it is thought undifferentiated stem cells reside), lower intermediate fragment, and in the bulb-containing fragment (an area with high mitotic activity containing a more differentiated pool of keratinocytes). In anagen follicles, high levels of telomerase activity were found almost exclusively in the bulb-containing fragment of the follicles, with low levels of telomerase in the bulge area (intermediate fragments) and gland-containing fragment. In comparison, catagen follicles had low levels of telomerase activity in the bulb-containing fragments as well as in other compartments. Such observations indicate that, in anagen hair follicles, the fragments containing cells actively dividing (e.g., transient amplifying cells) express telomerase activity, whereas fragments containing cells with low mitotic activity, for example, quiescent stem cells, express low levels of telomerase activity.

Adult↗
PubMed1996

Chromosome end-to-end associations and telomerase activity during cancer progression in human cells after treatment with alpha-particles simulating radon progeny.

Chromosome end-to-end associations seen at metaphase involve telomeres and are commonly observed in cells derived from individuals with ataxia telangiectasia and most types of human tumors. The associations may arise because of short telomeres and/or alterations of chromatin structure. There is a growing consensus that telomere length is stabilized by the activity of telomerase in immortal cells; however, it is not clear why some immortal cells display chromosome end-to-end associations. In the present study we evaluated chromosome end-to-end associations, telomere length and telomerase activity with the tumorigenic status of human bronchial epithelial cells immortalized with human papillomavirus. Oncogenic transformation was initiated using radon simulated alpha-particles and cells evaluated as primary, secondary and metastatic transformants. The fewest chromosome end associations and lowest telomerase activity were observed in the parental immortalized cells. However, increased levels of telomerase activity were detected in alpha-particle survivors while robust telomerase activity was seen in the tumorigenic cell lines. The tumorigenic cells that were telomerase positive and had the highest frequency of cells with chromosome end-to-end associations were also metastatic. No correlation was found between telomere length and the different stages of carcinogenicity.

Ataxia Telangiectasia↗
PubMed1996

Experimental elongation of telomeres extends the lifespan of immortal x normal cell hybrids.

Hybrids between immortal cells that express telomerase and normal cells that lack telomerase have a limited lifespan. We demonstrate that telomerase is repressed in such hybrids. Treatment of immortal human cell lines with certain oligonucleotides resulted in telomere elongation. We took advantage of this observation to test the hypothesis that elongation of telomeres would extend the lifespan of cells in culture. An immortal human cell line was treated with an oligonucleotide to lengthen its telomeres and then was fused with mortal cells. The lifespan of these hybrid cells was longer than that of the hybrids in which telomeres had not been elongated. These observations provide the first direct evidence supporting the hypothesis that telomere length determines proliferative capacity of human cells.

Base Sequence↗
PubMed1996

Telomerase activity in human germline and embryonic tissues and cells.

Telomerase is a ribonucleoprotein that synthesizes telomere repeats onto chromosome ends and is involved in maintaining telomere length in germline tissues and in immortal and cancer cells. In the present study, the temporal regulation of expression of telomerase activity was examined in human germline and somatic tissues and cells during development. Telomerase activity was detected in fetal, newborn, and adult testes and ovaries, but not in mature spermatozoa or oocytes. Blastocysts expressed high levels of telomerase activity as did most human somatic tissues at 16-20 weeks of development with the exception of human brain tissue. This activity could no longer be detected in the somatic tissues examined from the neonatal period onward. Neither placenta nor cultured fetal amniocytes contained detectable telomerase activity. Fetal tissues explanted into primary cell culture showed a dramatic decline in telomerase activity which became undetectable after the first passage in vitro. Elucidation of the regulatory pathways involved in the repression of telomerase activity during development may lead to the ability to manipulate telomerase levels and explore the consequences both for cellular aging and for the survival of cancer cells.

Base Sequence↗
PubMed1996

Monoclonal antimyogenin antibodies define epitopes outside the bHLH domain where binding interferes with protein-protein and protein-DNA interactions.

We have developed a panel of monoclonal antibodies against rat myogenin, a skeletal muscle regulatory protein of the bHLH family. Some of these monoclonals have been widely used by others, and details of their production are presented. Mapping the epitopes by immunoprecipitation of myogenin deletion mutants demonstrates that this panel recognizes epitopes spanning the entire molecule outside the HLH region. Four antibodies against epitopes outside the bHLH region interfere with the binding of myogenin/E-protein heterodimers to DNA sequences containing the myogenin heterodimer consensus recognition site. Three of these epitopes are partially masked in the heterodimers; antibody binding to these epitopes reduces the interactions between myogenin and E12. This suggests that surfaces outside the HLH dimerization domain may contribute to the stability of myogenin/E12 complexes. The binding of one antibody to its epitope did not appear to affect the myogenin/E12 interaction but nonetheless interfered with the binding of the complex to DNA, suggesting that this epitope lies near to a surface occupied by DNA.

Animals↗
PubMed1996

Inhibition of human telomerase activity by peptide nucleic acids.

We report the inhibition of human telomerase activity by peptide nucleic acids (PNAs). PNAs recognize the RNA component of human telomerase (hTR) and inhibit activity of the enzyme with IC50 values in the picomolar to nanomolar range. Inhibition depends on targeting exact functional boundaries of the hTR template and is 10- to 50-fold more efficient than inhibition by analogous phosphorothioate (PS) oligomers. In contrast to high selectivity of inhibition by PNAs, PS oligomers inhibit telomerase in a non-sequence-selective fashion. These results demonstrate that PNAs can control the enzymatic activity of ribonucleoproteins and possess important advantages relative to PS oligomers in both the affinity and the specificity of their recognition. These observations should facilitate the development of effective inhibitors of telomerase activity and affinity probes of telomerase structure.

Base Sequence↗
PubMed1996

Refining the telomere-telomerase hypothesis of aging and cancer.

While there has been substantial experimental evidence in support of the telomere-telomerase hypothesis of aging and cancer, it has been suggested that the theory has been oversimplified to the exclusion of alternative mechanisms in the progression of cancer. This review strives to present an overview of some of the areas that have not been well explained and to indicate where multiple interpretations of the data are possible.

Aging↗
PubMed1996

Age-dependent alterations of c-fos and growth regulation in human fibroblasts expressing the HPV16 E6 protein.

Normal human cells in culture become senescent after a limited number of population doublings. Senescent cells display characteristic changes in gene expression, among which is a repression of the ability to induce the c-fos gene. We have proposed a two-stage model for cellular senescence in which the mortality stage 1 (M1) mechanism can be overcome by agents that bind both the product of the retinoblastoma susceptibility gene (pRB)-like pocket proteins and p53. In this study we determined whether the repression of c-fos at M1 was downstream of the p53 or pRB-like "arms" of the M1 mechanism. We examined c-fos expression during the entire lifespan of normal human fibroblasts carrying E6 (which binds p53), E7 (which binds pRB), or both E6 and E7 of human papilloma virus type 16. The results indicate a dramatic change in cellular physiology at M1. Before M1, c-fos inducibility is controlled by an E6-independent mechanism that is blocked by E7. After M1, c-fos inducibility becomes dependent on E6 whereas E7 has no effect. In addition, a novel oscillation of c-fos expression with an approximately 2-h periodicity appears in E6-expressing fibroblasts post-M1. Accompanying this shift at M1 is a dramatic change in the ability to divide in low serum. Before M1, E6-expressing fibroblasts growth arrest in 0.3% serum, although they continue dividing under those conditions post-M1. These results demonstrate the unique physiology of fibroblasts during the extended lifespan between M1 and M2 and suggest that p53 might participate in the process that represses the c-fos gene at the onset of cellular senescence.

Aging↗
PubMed1996

Telomerase activity in human cancer.

The chromosome ends are specialized nucleoprotein structures called telomeres, which are essential for stable chromosome maintenance. In tumor-derived cell lines telomeres are maintained by the ribonucleoprotein enzyme telomerase. Telomerase activity is repressed in almost all normal human somatic cells. Due to the end replication problem, progressive telomere shortening occurs in normal somatic cells, leading to a limited replicative capacity and eventually resulting in cellular senescence. In the presence of viral oncogenes or some somatic mutations that block cellular senescence, cells continue to divide and telomere erosion continues. This continuing telomere erosion ultimately leads to the activation of telomerase, a necessary event for the sustained growth of most human tumors.

Aging↗
PubMed1996

Regulation of telomerase activity in immortal cell lines.

Telomerase is a ribonucleoprotein whose activity has been detected in germ line cells, immortal cells, and most cancer cells. Except in stem cells, which have a low level of telomerase activity, its activity is absent from normal somatic tissues. Understanding the regulation of telomerase activity is critical for the development of potential tools for the diagnosis and treatment of cancer. Using the telomeric repeat amplification protocol, we found that immortal, telomerase-positive, pseudodiploid human cells (HT1080 and HL60 cells) sorted by flow repressed in quiescent cells. This was true whether quiescence was induced by contact inhibition (NIH 3T3 mouse cells), growth factor removal (bromodeoxyuridine-blocked mouse myoblasts), reexpression of cellular senescence (the reversibly immortalized IDH4 cells), or irreversible cell differentiation (HL60 promyelocytic leukemia cells and C2C12 mouse myoblasts). Taken together, these results indicate that telomerase is active throughout the cell in dividing, immortal cells but that its activity is repressed in cells that exit the cell cycle. This suggests that quiescent stem cells that have the potential to express telomerase may remain unaffected by potential antitelomerase cancer therapies.

3T3 Cells↗
PubMed1996

Telomeres and telomerase in human leukemias.

There is increasing evidence supporting the hypothesis that telomere shortening both in vitro and in vivo, is the clock that counts cell divisions and determines the onset of cellular senescence. Cells that overcome the normal senescence mechanisms do so by stabilizing telomere length, probably due to the activity of telomerase, a ribonucleoprotein enzyme that synthesizes telomeric repeats. Most human primary tumors contain telomerase, while the cells of most normal tissues lack this activity. A hypothesis gaining prominence is that the activation of telomerase is necessary for the sustained growth of most solid tumors. Since normal hematopoietic stem cells and some of their progeny already express telomerase activity, it is important to consider whether or not telomere shortening and telomerase activity play any role in cancer progression in various forms of leukemia. This review includes a discussion of the utility of telomere length and/or telomerase activity measurements in the diagnosis and prognosis of leukemia as well as the potential value of antitelomerase therapy for the leukemias.

Base Sequence↗
PubMed1996

Telomerase activity in human acute myelogenous leukemia: inhibition of telomerase activity by differentiation-inducing agents.

The terminal regions of human chromosomes, the telomeres, shorten with each cell division in most normal somatic cells. Telomerase, a ribonucleoprotein that synthesizes telomeric DNA onto chromosomal ends, is activated in germline cells and almost all tumor cells. Telomerase activity maintains the stability of telomere length, resulting in indefinite cellular proliferation (immortality). In the present study, telomerase activity was analyzed in leukemic mononuclear blood cells obtained from 56 patients with acute myelogenous leukemia (AML) with known cytogenetic alterations. Heterogenous levels of telomerase activity were observed and generally correlated with cytogenetic status. Patients with 11q abnormalities and -5/-7 (unfavorable cytogenetics) tended to have high telomerase activity compared with cells obtained from AML patients with other types of cytogenetics. Additional studies with a larger cohort of patients will determine whether these differences are statistically significant. Chemotherapy agents that result in differentiation of leukemic cells also resulted in inhibition of telomerase activity. Knowledge of telomerase activity in patients with AML, before and throughout therapy, may have clinical utility for following disease progression and may predict early cancer relapse.

Adult↗